1 files changed, 11 insertions, 4 deletions
diff --git a/ffi/src/lib.rs b/ffi/src/lib.rs
index 7ffcb00..4682136 100644
--- a/ffi/src/lib.rs
+++ b/ffi/src/lib.rs
@@ -3,11 +3,18 @@ pub use constants::*;
 
 #[unsafe(no_mangle)]
 #[allow(nonstandard_style)]
-pub extern "C" fn JV_FreeString(ptr: *mut libc::c_char) {
-    if ptr.is_null() {
-        return;
-    }
+/// # Safety
+///
+/// This function must be called with a pointer that was obtained from
+/// `JV_Const_*` functions or `std::ffi::CString::into_raw()`. The pointer
+/// must not be null unless it was explicitly returned as null from the
+/// allocating function. After calling this function, the pointer becomes
+/// invalid and must not be used again.
+pub unsafe extern "C" fn JV_FreeString(ptr: *mut libc::c_char) {
     unsafe {
+        if ptr.is_null() {
+            return;
+        }
         drop(std::ffi::CString::from_raw(ptr));
     }
 }